Sunday, May 14, 2017

Astronauts Complete 200th ISS Spacewalk

Fischer during EVA-42. Photo Credit: NASA TV

For the 200th time in nearly two decades, two people aboard the International Space Station donned spacesuits and ventured outside to perform a spacewalk. Problems during preparations for the excursion, however, ultimately caused it to be cut short by more than two hours.

NASA astronauts Peggy Whitson and Jack Fischer – Expedition 51 commander and flight engineer, respectively – exited the airlock more than an hour later than planned at 9:08 a.m. EDT (13:08 GMT) on May 12. This was due to the discovery of a small water leak in a servicing and cooling umbilical. While the line was not part of the crew’s spacesuits, ground teams still needed to understand the nature of the leak.

It was determined that the EVA could proceed with only one working umbilical, but consumables, such as water, air, and battery levels, needed to be watched carefully to preserve margins. As such, the spacewalk was cut from a planned 6.5 hours to just over four hours.

Extravehicular activity 42 (EVA-42), as this spacewalk was called, began when the airlock pressure dropped to 1 bar, rather than when the crew switched to battery power, as is typical for U.S. spacewalks. Once the hatch to the Quest airlock was open, the two left and went in separate directions.

“Oh my gosh, this is beautiful,” Fischer said once he had a moment to look at Earth. “The biggest slice of awesome pie I’ve ever seen.”

Whitson radioed to Fischer to ask why he didn’t use “awesome sauce”, which is one of his favorite expressions.

“How about ginormous fondu pot bubbling over with piping hot awesome sauce?” Fischer said.

Whitson, who was the lead spacewalker and wore the suit with red stripes, went to her worksite on the S3 truss segment. There she began working to replace an avionics box on Express Logistics Carrier (ELC) 4. The ExPrESS Pallet Control Assembly (ExPCA), which is pronounced “ex-pecka”, had never been replaced in space before.

To assist her, Fischer, who wore the suit with no stripes, grabbed a foot restraint and attached to to the end of the robotic Canadarm2. He was then moved over to the same area Whitson was located.

The ExPCA is one of the units that provides power, command, and data distribution capabilities to the ELCs and orbital replacement units. This particular avionics unit was brought up to the outpost aboard the recently arrived S.S. John Glenn (OA-7 Cygnus) spacecraft.

Because this replacement part was necessary for the spacewalk to commence, the excursion was delayed by more than a month to wait for the launch of the cargo craft. The duo made quick work in replacing it once they were both at the site.

The next two tasks were the repair of insulation on the Japanese robotic arm on the Kibo module and the installation of a data collector on the Alpha Magnetic Spectrometer (AMS-2), which is a particle physics experiment that has been attached to the outpost since 2011.

For this, each astronaut took a task. Whitson made her way to AMS-2 while Fischer went toward Kibo.

Whitson’s task involved installing a telemetry path for engineers to investigate the performance of AMS-2’s cooling pump as well as to test a data port that hasn’t been active since the experiment was installed.

AMS-2 was originally meant to be a short-term experiment. It was to be flown back to Earth in the payload bay of a Space Shuttle after several years in orbit. However, when the decision was made to retire the orbiters, engineers worked to transform the unit into a long-term experiment.

Even so, the pumps are showing signs of degradation and will eventually need to be replaced, likely over several spacewalks. When that occurs, engineers want to install active control pumps.

While Whitson was working on AMS-2, Fischer repaired the insulation on the Japanese robotic arm. Once they were both done, they both worked on installing a debris shield around the base of Pressurized Mating Adapter 3, which was recently relocated to allow for future commercial crew vehicles to dock with it.

PMA-3 still needs an International Docking Adapter to be launched and attached before it is ready to support the Commercial Crew Program. IDA-3 is expected to launch sometime next year inside the trunk of a SpaceX Dragon capsule. Once installed, it will be a backup port to the one that was installed in the summer of 2016.

Once complete, the spacewalking time was approaching four hours. Managers decided to cancel several tasks, including taking pictures of AMS-2 and the recently installed SAGE-III, and told the astronauts to clean up their work area and make their way back to the airlock.

Once re-pressurization began, which occurred at 1:21 p.m. EDT (17:21 GMT), the spacewalk officially ended. The two had been outside for 4 hours, 13 minutes.

This brought Whitson’s total spacewalking time to 57 hours, 35 minutes; the fifth place behind former astronaut John Grunsfeld’s 58 hours, 35 minutes. She was just under an hour short of making it into the top three for most time spent spacewalking.

EVA-42 was the 200th spacewalk in support of the ISS assembly and maintenance, bringing the total time to 1,247 hours, 55 minutes. The first spacewalk occurred during the STS-88 mission in December 1998 when the crew of Space Shuttle Endeavour worked to attached the first two modules of the ISS: Zarya and Unity.

Written by: Derek Richardson
Original source: spaceflightinsider.com

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